432 PllOCEEDINGS OP THE GEOIOGICAI SOCIETT. [JunO 5, 



1. That the causes which induce the extremes of climate in the 

 temperate zone of Northern Asia and America could not have existed 

 in Britain. Before this objection can hold good, it is necessary to 

 show what these causes are. Prevalence of wind in certain direc- 

 tions, writes Mr. Geikie (p. 166). This may be one of the causes; 

 biit at the same time it is one of the effects of change of temperature. 

 The vera causa of the extremes in both cases seems to me to be that 

 pointed out by Sir C. Lyell in the 12th chapter of the ' Principles' 

 (1867) — the extension of a large mass of land from the equator to 

 the polar circle. Such a mass of land extended from the range of 

 Atlas northwards to the snowy regions of Scandinavia during the 

 Pleistocene age (see Map, p. 436), the Mediterranean being reduced 

 to two land-locked seas, and the mainland of Africa being continued 

 on the one hand into Spain, and on the other, by Malta and Sicily, 

 into Italy, and Greece extending so far south as to embrace Candia. 

 Such an extent of land is surely an exact parallel to the two cases 

 which I have quoted above ; and climatal extremes must necessarily 

 have been the result of the substitution of land for such a large area 

 that is now covered by the sea. (See Map.) Mr. Geikie admits 

 that at that time the winters were very much colder than they are 

 now, because the higher mountains of Europe were also covered by 

 mers de glace. Can he deny that the above geographical change in 

 the Mediterranean area would have also left its mark in a higher 

 summer temperature, other causes being put out of sight, than now ? 

 The inference that the summer temperature (p. 166) would be lower 

 than at present in Britain, because there were glacier- areas in the 

 north and in the higher districts in Central Europe, is inconclusive, 

 since the mere existence of a glacier tells us nothing of the summer 

 heat of the surrounding regions. Could we predicate, for instance, 

 the temperature of the Subhimalayas from the contemplation of 

 the glaciers of the central ridge ? or the summer heat of Lombardy 

 or of Provence from the glaciers of the Alps? Glaciers merely 

 imply the existence of a certain line of mean annual temperature, 

 above which the snow accumulates, and from which they are pushed 

 down in some cases, as in New Zealand, to within a few hundred 

 feet of the sea. It is obvious, therefore, that any argument from the 

 Pleistocene glaciers to the summer heat is without value. All specu- 

 lations as to the prevalent wind at that remote time in diiferent 

 parts of Europe appear to me mere guesses and nothing else. 



2. The second objection is that the Hippopotamus is not a migra- 

 tory animal. Is this so ? It is true that its aquatic habits forbid its 

 migration over the vast arid plains of Southern Africa, like the An- 

 telopes ; but, on the other hand, direct evidence for or against its 

 migratory habits in a well- watered region is at present wanting. 

 The remains found in Nubia, and preserved in the British Museum, 

 certainly prove that once it ranged further north on the Nile than it 

 does now. So far the evidence is in favour of its being a migratory 

 animal. If its present range be compared with that during the 

 Pleistocene it is impossible to deny that it has migrated from Africa 

 to Yorkshire, or vice versd. - . . , 



